Differential pump



DO UGLA S 7 2,254,103

DAIFFERENTIALI, PUMP Filed April 16, 1936 GSheetSfiSheet 1 W INVENTEJR BY v 7. ya =WT U NEY.

Aug. 26, 1941. .1. K. DOUGLAS DIFFERENTIAL PUMP Filed April 16, 1936 G ShGGtS -ShGGt 2 mm mm W q 12 7// ON Q ON N o: m3 N m Rh a I I m4 Q\ hum m8 NW E h w. m 3 N a Q 9 ON Q km M N INVENTEIR JAMES K. DOUGLAS Aug. 26, 1941. J. K. DOUGLAS DIFFERENTIAL PUMP Filed-April 16, 1936 GSheets-Sheet-S R s n .Y T L E N G N E U H W U D. ID V m .N. k. K A S\ 5 2. vm @N M Wm J 8 m Q emm Q on m S ow 0Q 7 2 Q 9 .fl a e a 3K v2 k523 Q 9% v 04 NR N Ow 0w. NM. msa hs NW F NW N\ k Q @525 B5 w: ow w: 3 mfl mm a. w o 4 mfi w: J 1 h ow Q E: W: v: I. a: um \\\ow m: fl HI u .m Q\\ w a E i Patented Aug. 26, .1941

UNITED STATE DIFFERENTIAL PUMP James K. Douglas, Shorewood, Wis assignor to The Oilgear company. Milwauk poi-atlon of Wisconsin Application April 18, 1936, Serial m. 14,740 11 Claims. (01. 103-151) This invention relates to pumps of the type ordinarily employed for supplying liquid to hydraulic motors to drive-the same; A pump of this type has heretofore been so constructed that, when connected in circuit with a non-differential motor, the volume of-liquid returned to the pump cylinder from the circuit. is the same as the volume supplied by the pump to the circuit except for the volume lost due to leakage or slip.

The present invention has as an object to provide a pump which under tion will discharge into a hydraulic circuit a greater volume of liquid than its cylinders receive therefrom. g

A non-differential motor driven by liquid 'supplied thereto from" a pump embodying the present invention may have a-back pressure maintained thereon without passing the entire motor discharge through a resistance.

Other objects and advantages will appear from the description hereinafter given of a pump in which the invention is embodied. According to the invention in general aspects, the pump is so constructed that the number of its cylinders discharging into a hydraulic circuit is greater than the number of'its cylinders receiving liquid therefrom.-

The invention is exemplified by the pumps 11- lustrated somewhat schematically in the accomall conditions of opera-- ee, Wia, a cor-.-

nels through which liquid mayflow to and from an external circuit.

Fig. 10 is a diagram pump connected in circuit. with a differential motor, the reversing valve and the by-pass valve being shown in position to cause the motor to execute a working stroke.

Fig. 11 is a sectional view showing the reversing valve in position to cause the motor to execute a return stroke. V

Fig. 12 is a sectional view showing the by-pass valve in position to by-pass the pump and thereby stop the motor.

'For the purpose of'illustration, the invention is shown embodied in pumps of the rolling piston type describedand claimed in Ferris Patent No.

2,074,068 to which attention is directed for an explanationof the characteristics of rolling piston pumps. I Figs. 1 to 5 As shown-in these figures, ,the pump has its mechanism arranged within and carried by a casing I which may be arranged upon and sup-' panying drawings in which the views are as follows: Fig. I is a view taken on the line I-I of Fig. 2

and illustrating in central longitudinal section a reversible differential pump in which the inven-. tion is embodied.

Fig. 2 is a transverse section taken on the line 2-2 of Fig. 1.

Fig. 3 is a. transverse section taken on line Fig. 4 is a sectional plan view taken on the line 4-4 of Figs. 1 and 3 and showing the channels through-which liquid may flow to and from an external circuit.

Fig. 513 a diagram. showing the pump connected in circuit with a non-differential motor.

Fig. Bis a view taken on the line 0-4 of Fig. 'l

and illustrating in central longitudinal section a non-reversible differential vention is embodied.

Fig. his a transverse section taken on the line |'-1 of Fig. 8.

Fig. 8 is a transverse section taken on the line H of Pig. 6.

Fig. 9 is a sections! line H of Figs. 6 and sand pump-in which'the inplan view taken on the showing the chanported by a reservoir 2 containing the supply of liquid such as-oil. Casing I is closed at its rear end by an end wall 3 of substantial thickness and at its front end by a removable front head 4 which is fastened to the end of easing I as by means of bolts 5. I

Rear wall '3 has rigidly secured therein the rear part o'ia valve shaft or pintle 8 the front part of which extends into casing' I and has formed therein two diametrically opposed main ports 'I and 8 and two diametricallyv opposed auxiliary p rts 9 and I0.

The front part of pintle thereon a rotatable cylinder barrel I I which'is ordinarily composed of a plurality of rigidly connected concentric sections and provided with a plurality of main cylinder ports I2 and a plurality of auxiliary cylinder ports II.

Ports I2 are arranged in a circular row so that each'port Ilmay'register with pintle ports 'I and Q alternately as cylinder barrel II rotates. Likewise, cylinder ports I! are arranged in a circular row so that each port It may register with pintle ports I and III alternately as cylinder barrel II rotates. In order that no two cylinder contains an odd ports mayopen to a pintle intake portand to a pintle discharge port simultaneously. each row shown.

Cylinderbarrel n isadapted to be rotated by showing the non-reversible 6 has closely fitted number of ports, nine being head 4 and is iournaled near its outer end in a bearing I3 carried by front head 4 and at its inner end by a bearing 1 3 arranged in the end ofv pintle 3. Shaft l4 drives cylinder barrel ii through a driver II which is splined on shaft M and connected to cylinder barrel H by a universal driving connection l3.

Cylinder barrel II is provided with a plurality of radial cylinders l 3 which are shown arranged in four circular rows with eighteen cylinders in each row. The cylinders in the three rear rows communicate with ports l2 and the cylinders in the, front row communicate with ports I3, as, shown in Fig. 1, and each two adjacent cylinders in each row communicate with each other. as shown in Fig. 2, so that each port i2 serves six cylinders and each port l3 serves two cylinders.

Each cylinder l3 has fitted therein a piston 23 having an arcuate contact face upon its outer end to engage a thrust ring 2| fixed upon the inside of an annular thrust member 22 which substantially encloses cylinder barrel ll.

Thrust member 22 is supported at its front and rear ends, respectively, in two anti-friction bearings 23 and 24 carried by a slide block '23 which is supported in casing I as by means of four slide plates 23 fastened to slide block 23 and four slide plates 21 fastened to the upper and lower walls of casing l. The arrangement "is such that slide block 23 may be shifted transverse to the axis of pintle 3 but is restrained from any vertical movement. v

Slide block 23 is adapted to be shifted in one direction or the other by two servo-motors one of which has its piston 23 fastened to one side thereof and the other of whichhas its piston 23 fastened to the other side'thereof. Piston 23 is fitted in a cylinder 33 which is formed in one side wall of casing l and closed at its outer end by a head 3| having an adjusting screw 32 threaded therethrough for limiting the movement of slide block 23in on direction. Piston 23 is fitted in a cylinder 33 which is formed in the other side wall of casing] and closed at its outer end by a head 34 having an adjusting screw 33 threaded therethrough for limiting the movement of slide block 23 in the opposite direction.

Slide block 23 may be shifted in one direction by liquid supplied to cylinder 33 through a pipe 36 which is connected to head 3|, and it may be shifted in the opposite direction by liquid supplied to cylinder 33 through a pipe 31 which is connected to head 34.

Liquid for operating servo-motors 23-33 and 23-33 may be suppliedzby an auxiliary pump such as an ordinary gear pump having its driving gear 43 fastened upon drive shaft l4 and its driven gear 4| fastened upon a stub shaft 42 which is fixed in front head 4. Gears 43 and 4| are arranged ina pump chamber 43 which .is formed in front head" 4 and closed at its rear by a plate 44 bolted or otherwise secured to front head 4.

Gear pump 43- has not been illustrated nor described in detail as it is of ordinary construction and as it is commonpractice to arrange such pumps in the manner shown. It is deemed sufficient to state that it draws liquid from reservoir 2 through a suction channel 43 and discharges barrel I I ing screw 33 and, if pressure liquid is supplied through pipe 31 to cylinder 33, piston 23 will shift slide block 23 toward the left until piston" member 22 is offset from the cylinder barrel axis,

each piston 23 will move progressively outward during one half-revolution of cylinder barrel II and inward during the other half-revolution thereof, the frictional contact between pistons 23 and thrust rings 2| causing thrust member 22 to rotate substantially in synchronism with cylinder Liquid will fill the cylinders as the pistons move outward and be expelled from the cylinders as the pistons move inward, andthe pump will deliver liquid in a direction and at a rate determined by the direction .and the distance the axis of thrust member 22 is offset from the cylinder barrel axis.

If slide block 23 is shiftedltoward the right and cylinder barrel II is rotated in a counterclockwise direction as viewed in Fig. 2, the pistons in the upper half of cylinder barrel II will move progressively inward and expel liquid from their cylinders into pintle ports I and 3 ata rate determined by the adjustment of screw 33, and liquid will fiow through pintle ports 3 and I3 and fill the cylinders in the lower half of cylinder barrel II. If slide block 23 is shifted toward the left, liquid will flow to the cylinders in the upper half of cylinder barrel ll through'pintle ports I and 3 and be expelled into pintle ports 3 and I3 from the cylinders in the lower half of cylinder barrel II.

The cylinders in the three rearrows in cylinder barrel II are adapted to deliver liquid directly to and receive liquid directly from an external circuit, two pipes 33 and 3| of which maytends downward and then laterally in rear wall 3 into communication with a passage 31 which extends radially into pintle 3 and then longitudinally thereof into communication with pintle port 3. v

The arrangement is such that the cylinders in the three rear. rows of cylinder barrel ll discharge either through port 1' into pipe 33 or through portlj into pipe 5| and are supplied with liquid either through pipe 3| and port 3 or ,through pipe 33 and port 7 depending upon the versed, that is, in order that the front row of it into a low pressure supply channel 43 as shown schematically in Fig. 5.

If pressure liquid is supplied through pipe 33 to cylinder 33, piston 23 will shift slide block 23- toward the right until piston 23 engages adiustcylinders may deliverliquid into either pipe 33 or pipe 3| and be supplied with liquid from reservoir 2 regardless of which pipe they deliver liquid into, the pump isprovided with an automatic switch valve 33 which has a centralhead or piston 3| and two end heads or pistons 32' and 33 formed thereon and closely fitted in a bore 88 formed in rear wall 8 transversely thereof.

Valve pistons 82 and 88 control communication between bore 88, and the two ends of a passage 55 which is formed in rear wall 8 below bore 88 and parallel thereto.. Passage 85 communicates through a check valve 88 with a suction pipe 81 which extends downward into the liquid in reservoir 2. v

Valve piston 8| controls communication between a passage 88 and a passage 58, between passage 88 and a passage 'l8 and between passage 88 and a passage 1 I, all four of which are formed in rear wall 8.

Passages 88 and 58 connect bore 88 to passages 52 and 58 respectively. Passage 18 extends forward to a point beyond passage 88 and then it extends upward into communication with a passage which isiformed inpintle 8 and communicates with port 8. Passage extends forward to a point beyond passage 58 and then extends upward into communication witha passage 13 which is formed in pintle 8 and communicates with port i8.

In order that valve 68 may be shifted automatically when the direction of liquid flow is reversed, passage 18 is connected to the left end of bore 88 by a passage I4 formed in rear wall 3, and passage II is connected to the right end of bore 88 by a passage 15 formed in rear wall 3.

when the axis of thrust member 22 is offset toward the right from the cylinder barrel axis and cylinder barrel II is rotated in a counterclockwise direction as viewed in Fig. 2, the cylinders will discharge into pintle ports 1 and 8 and be supplied with liquid through pintle ports 8 and M as previously explained. Ihe liquid discharged into port I will flow. through passages 55, 58 and 52 into pipe 58 and the liquid discharged into port 9 will flow through passages 12,

I8 and 18 to the left end of bore 88 and move valve 88 toward the right to the position shown in full lines in Fig. 3 and then it will flow from passage through bore .88 and passages 88 and 52 into pipe 58 so that the output of all of the cylinders is combined into a single stream..

At the same time, the cylinders in the three rear rows will be. supplied with liquid from the external circuit through passages 58, 58 and 5l and ports 8 and I2, and the pistons in the front 6 row will draw liquid into their cylinders from reservoir 2 through suction pipe 81, check valve 88, passage 85, bore 88, passages II and I3 and 7 p rts and I8.

- When slide block of thrust member 22 is offset toward the left 25 is shifted so that the axis.

from the axis of cylinder barrel II, the cylinders will discharge into pintle ports 8 and i8 and be supplied with liquid 8. The liquid discharged into port 8 will flow through passages 51, 58 and 58 into pipe 5| and the liquid through passages 13, H and 15 to the right end 88 and move valve 88. toward the left to the position shown in dotted lines in Fig. 3 and then it will flow from passage 1| through bore 88 and passages 88. 58 and 58 into pipe 5| so that through pintle ports I and discharged into port .II will. flew.

The pump thus delivers its entire output in a single stream and has apart of its cylinders.

supplied with liquid from one source and the remainder of the cylinders supplied with liquid from a different source in either direction of pump delivery.

For the purpose of illustration, the pump is shown in Fig. 5 as being connected by pipes 58 and 5| to opposite ends of the cylinder 88 of a non-differential motor and as having its servomotor pistons 28 and 88 operated by liquid supplied to cylinders 88 and 88 from gear pump 88- under the control of a reversing valve 8| to the casing of which pipes 88, 81 and 48 are connected.

Cylinder 88 has a piston, 82 fitted therein and connected to two piston rods 88 and 88 which extend through opposite ends of cylinder 88 and which are equal in cross sectional area so that, during operation of the motor, the volume exhausted'from one end of cylinder 88 is substantially the same as the volume of motive liquid supplied to the other end thereof. I

Since all four rows of pump cylinders discharge through one of pipes 58 and 5| to the motor and only three rows of pump cylinders are supplied with liquid therefrom through the other of pipes 58 and 5|, as previously explained, and since the volume discharged bythe motor into one of pipes 58 and 5| is substantially equal to the volume supplied thereto through the other of pipes 58 and 5|, it follows that more liquid is discharged by the motor than can be received by the three rows of pump cylinders connected thereto. 1

The liquid discharged by the motor in excess of the liquid that can be received by the three rows of pump cylinders is exhausted through an antijump valve 85 into a drain pipe 88 which discharges into reservoir 2.

lin order that the liquid discharged by the motor in excess of pump requirements may be exhausted through anti-jump valve 85 in either direction of motor actuation, valve 85 is adapted to be connected to the discharge end of. cylinder ends thereof and by a pipe 88 to pipe 5| intermediate the ends thereof.

The function of valve 85 is to prevent a sudden variation in motor load from causing a material variation in motor speed as fully explained in Patent No. 2,071,781. Valve 8|, which enables valve 85 to function during actuation of the motor in either direction, and valve 85 have not been shown in detail as they are fully illustrated and described in said patent. It is deemed sufficient to state that, when reversing valve 8| is in one position, liquid from gear pump 88-8| the output of all of the cylinders is combined into a single stream.

At the same time, the cylinders in the three rear rows-will besupplied with liquid from the" external circuit through passages 58, 58 and 55 and ports I and I8, and the pistons in the front row will draw liquid into their cylinders from reservoir 8 through suction pipe 81, check valve will flow through pipe 88. valve 8| and pipe 88 to cylinder 88 and move slide block 25 toward the right to the-position-shown in Fig.2. Then the output of all of the cylinders will flow through pipe 58 to the left end of cylinder 88 and force piston 82 tqward the right 7 Piston .88 will discharge liquid from the ri ht end of cylinder 88 into pipe 5|. Enough of this dis harge liquid to fill the pump cylinders in the three rear rows will flow thereto and theremainder of the discharge liquid will flow through pipe 89, valve 8|, pipe 81, anti-jump valve 85 and drain pipe 88 to reservoir 2.

A predetermined pressure is required to open anti-jump valve 85 which thereby causes a back pressure to be maintained upon motor piston 82 and the three rear rows of pump cylinders to be supercharged. It also causes a much higher momentary back pressure to be created in response to piston 82 tending to move at a speed greater than the predetermined speed as fully explained in Patent No. 2,071,781 referred to above.

When reversing valve 8| is shifted to its other position, the transmission will operate in the.

same manner but in the opposite direction. That is, liquid from gear pump 48- will flow through pipe 48, valve 8| and pipe 31 to cylinder 83 and shift slide block 25 toward the left and thereby cause the pump to deliver its entire out- Figs. 6- to 12 spectivelmwith two passages 51 and 13 which are formed in pintle 8' longitudinallythereof.

Passage 51' communicates at its rear end with passage 58 which is formed in rear wall 3 and extends transversely thereof into communication with a passage 53" which exterds rearward through the .end of rear wall 8- to permit the three rows of pump cylinders to be supplied with liquid from the external circuit to which passage 53" is connected.

Passage 13 communicates at its rear end with a passage 1| which may be connected direct to reservoir 2 through check valve 58 and suction pipe 81 but which, in order to permit the pump to function as a non-difierential pump, is shown connected to a bore I82 which is formed in rear wall '8 and has a switch valve I88 arranged therein.

Bore I82 is connected to passage 58 by a passage 88 and to suction-pipe 81 through a passage 85* and check valve 88. Valve I88 is provided with two spaced apart-heads or pistons I84.

and I85 which are closely fitted in bore I82.

1 When valve I88 is in .the position shown in Fig. 8, valve piston I84 blocks the end of passage 88' so that liquid returned: to the pump from an external circuit may flow 'to the threerear rows of cylinders only and the front row The pump shown in these figures is nonreversible but many of its parts are exactly the same as and other of its parts are similar to the corresponding Parts of the pump shown in Figs. 1 to 5. Consequently, like parts have been indicated by like reference numerals and no further description thereof will be given while similar parts have been indicated by corresponding reference numerals with the exponent "a" added.

Since the pump is non-reversible, it has been shown as having its slide block 25 arranged within a casing I and provided with an adjusting screw I88 which extends outward through a cylinder 83 formed in the side wall of the casing. Screw I88 has threaded thereon a hand wheel I8I which is Journaled in and restrained from axial movement by a head 24 which is fastened to the outer end of cylinder 28'. Rotation of hand wheel I8I will cause slide block 25 to be moved transversely of easing I and thereby vary pump displacement.

The pump has its cylinder barrel II journaled upon a pintle 8' which is rigidly secured in the rear wall 8". of the pump casing I. Since the pump is non-reversible. all of the pump cylinders I9 may discharge into a single pintle port or into two communicating ports. As shown, the pump cylinders discharge into pintle ports 1" and- 8 which communicate with each other and of cylinders must be supplied entirely from reservoir 2. When valve I88 is shifted toward the right, passage 88" will be open to passage 1| andall of the pump cylinders may be supplied from an external circuit or they may draw theirsupply either entirely or in part from'reservoir 2. For the purpose of illustration, the pump is shown in Fig. 10 as being employed to.drive a differential hydraulic motor consisting of a stationary cylinder 8- and a piston III which is fitted in cylinder I I8 and has a single piston rod II2 fixed thereto and extending through one end only of cylinder -II8-. I

Operation of motor IIII-I II is controlled by a reversing valve 2 arranged in a valve casing III and by a by-pass valve 5 arranged in a valve casing 8. For simplicity in illustration,

' valves II8 and.-I I5 have been shownas being of with two passages 55 and 12* formed in pintle 8'- longitudinally thereof.

Passages 55" and 12' communicate at the rear ends thereof with a passage 54' which is formed in rear wall 3' and extends transversely thereof the rotary type but in practice reciprocating or piston valves are'preferably employed.

Reversing valve casing Ill is-connected by two pipes H1 and 8 to oppositeends of cylinder II8, by a pipe III to by-pass valve casing II8, by

a pipe I28 to passage 82 in the rear wall 3' ofthe pump casing, and by a pipe I2I to a drain pipe I22 which discharges into reservoir 2. Pipe I2I 'is connected to casing II between pipes H1 and tween pipe I28 and valve casing II, pipe I28 is connected by a pipe I21 to the inlet of an antijump valve I28 which has its outlet connected by a pipe I28 to drain pipe I2I. Anti-jump valve I28 is exactly the same as anti-jump valve previously described and no further'description thereof will be given.

When valve I82 is in the position shown in Fig: 8, valves H8 and II! are in the positions shown 'in Fig. 10 and cylinder barrel II is rotating, liquid discharged from all four rows of pump cylinders will fiow through pintle passages 55 and 12 passagefl, passage 82*. pipe I24 by-pass valve casing II8, pipe 8, reversing valve casing |I4 and pipe III to the left end of cylinder Ill and force piston Ill toward the right on a working" stroke. v

Piston III will expel liquid from the right end of cylinder ll: through pipe H8 and reversing 5 valve casing Ill into pipe I20. Enough of this liquid to fill the three rear rows of pump cylinders will fiow thereto from pipe I20 through passages 53', 56* and 51, and the remainder of the expelled liquid will be forced from pipe I20 through pipe I21 and anti-jump valve I28 and then fiow through pipes I29, l2l and I22 to reservoir 2. At the same time, the front row of pump pistons will draw liquid into their cylinders from reservoir 2 through pipe 61, check valve 68,

passage 65, bore I02 and passages II and 13'.

Since anti-jump valve I28 will not open until the pressure in pipe I reaches a predetermined value, it will cause a predetermined back pressure to be maintained on piston III during move- 20 ment thereof at or near the predetermined speed, and it will cause a very high back pressure to be momentarily exerted thereon in response to piston I l I tending to jump forward as fully explained in my Patent No. 2,071,781 referred to above.

The hydraulic motor driven by the pump may be so proportioned that there will be little loss of power due to forcing liquidthrough the antijump valve. For example, if three-fourths of the pump cylinders are supplied with liquid from the 30 motor and one-fourth of the pump cylinders are supplied with liquid from the reservoir, and if the ratio between the cross-sectional area of piston rod I I2 and the cross-sectional area of piston III III) and piston III will expel 3.1 volumes of which 3 volumes are consumed by the three rows of cylinders and only ,1 volume is exhausted through anti-jump valve I28.

When reversing valve I I3 is shifted to the positlon shown. in Fig. 11, the liquid discharged by the pump will flow through pipe I24, by-pass valve casing IIS, pipe II9, reversing valve casing Ill and pipe Ill to theright endof cylinder Ill and move piston III toward the left and cause it toexpel liquid from the left end of cylinder ll0 through pipe lll into reversing valve casing Ill.

A part of the expelled liquid will flow through pipe l2l| and communicating with passages to the three rear rows of pump cylinders and the remainder of the expelled liquid will flow into drain pipe I22 through resistance valve I22 which offers enough resistance to the flow of liquid therepipe I25 so that the liquid discharged by the pump may be in partreturned direct to the pump cylindersto fill the same andin part exhausted into reservoir 2, thereby preventing motor IlB-Illfrom operating.

' The invention herein set forth is susceptible of various modifications and adaptations without degi'ting. from the scope thereof as hereafter. cl ed.-

The invention is hereby claimed as follows:

1. Inap'ump havingan cutletandafirstand 76' a second inlet, the combination of a-plurality of cylinders, a piston fitted in each cylinder, means for reciprocating said pistons to cause the same to draw. liquid into said cylinders and discharge it therefrom, valve means for directing the liquid discharged from all of said cylinders to said outlet and for directing liquid from said first inlet to a part only of said cylinders and for directing liquid from said second inlet to the remainder of said cylinders, and means for reversing said pump without altering the number of cylinders deliver- .ing liquid to said .outlet' or the number of cylinders receiving liquid from said first inlet.

' 2. A differential pump, comprising a valve member having intake and discharge ports arranged therein, a rotatable cylinder barrel engaging said valve member and provided with a plurality 'of cylinder ports each of which communicates with an intake port and a discharge port alternately as said cylinder barrel rotates, a plurality of cylinders arranged in said cylinder barrel and each communicating with a cylinder port, a piston fitted in each cylinder, means for reciprocating said pistons during rotation of said cylinder barrel, said valve member being so constructed and connected in circuit that it combines the output of all of said cylinders and directs liquid from one source to a part only of said cylinders and liquid from another source to the remainder of said cylinders, and means for reversing said pump without altering the number of cylinders which receive liquid from each of said sources.

3. A diflerential pump, comprising a valve shaft or pintle having intake and discharge ports and passages arranged therein, a rotatable cylinder barrel Journaled upon said pintle and provided with a plurality of ports each of which communicates with an intake port and a disis .9:4, then during a given interval of time the 35 char alternately as said cylinder barrel' pump will deliver 4 volumes of liquid to cylinder rotates, a pluralityof cylinders arranged in said cylinder barrel andeach communicating with a cylinder port. a piston fitted in each cylinder, means for reciprocating said pistons during rotation of said cylinder barrel, said ports and passages being so arranged that the output of all of said cylinders may be combined into a single stream and that liquid may be supplied to a part only of said cylinders from one source and to the remainder of said'cylinders from a different source, and means for reversing said pump without altering the number of cylinders which receive licmid from each of said sources.

4. A differential pump, comprising a valve member having an intake port formed therein upon one side of the center thereof for connection to one side of an external hydraulic circuit, a second intake port formed therein upon the same side of the center thereof for connec-v tion to a separate source of fluid supply and at least one. discharge port formed therein upon the oppositesideof the center thereof for con-,

nectlon to the other side of said circuit, a rotatable cylinder barrel engaging saidvalve memher and provided with a plurality of ports each of which communicates with an intake port and a discharge port alternately as said cylinder barrel rotates, a plurality of cylinders arranged in said cylinder barrel and each communicating with 'a cylinder port, a piston fitted in each cylinder, means for reciprocating said pistons during. rotation of said cylinder barrel, and means for reversing --.said pump without altering the number of cylinders that are supplied with liquid from said separate, source.

- 5. A differential pump for-supplying liquid to a hydraulic circuit, comprising two separate sets of-plgtongand cyiindera'means for actuating galdplstons, means for. connecting the cylinders of onesettothe pressure andreturn sidesof 6 i said circuit alternately whereby the cylinders of that set receive liquid from the return side of said v pressure side of said circuit.

6; A diflerential pump, comprising a valve member provided in one half thereof with a discharge port and in the opposite halt thereoi with two intake ports having no communication with eachother, a rotatable cylinder barrel engaging said valve member and having a plurality cylinder ports arranged therein in two circular rows, the ports in one row communicating with one of said intake portsand said discharge port alternately and the ports in the other row communicating with the other of said intake ports and said discharge port alternately during rotation of said cylinder barrel, a plurality of cylinders arranged in said cylinder barrel and each communicating with a cylinder port, a piston fitted in each cylinder, means for reciprocating said pistons during rotation oi said cylinder barrel, and means for connecting said intake ports a to separate sources oi liquid supply.

7. A diiierential pump, comprising a valve member havingtwo intake ports and two discharge ports'iormed therein upon opposite sides of the center thereof, a rotatable cylinder bar rel engaging said valve member and having a plurality of cylinder ports arranged thereinin two circular rows, the ports in each row communicating with one intake port and one discharge port alternately as said cylinder barrel rotates. a plurality of cylinders arranged in said cylinder barrel and each communicating with a cylinder port, a piston fitted in each cylinder, means for reciprocatingsaid pistons during rotation 01 said cylinder barrel, means for connecting one of each oi. said intake and discharge ports to an external circuit, means for connecting the other discharge port to said circuit. and'means for connecting the other intake port to a separate source oi l quid sunp yv 8. A reversible diflerential pump, comprising a valve member having two intake ports and two discharge ports formed therein upon opposite sides of the center thereof, a rotatable cylinder supply selectively. responsive to reversal of liquid flow.

9. A reversible .diiierential pump, comp a valve shaft or pintle having two opposed main ports and two opposed auxiliary ports formed therein, a rotatable cylinder barrel iournaled upon said pintle and having a plurality oi cylinder ports arranged therein in two circular rows, the ports in each row communicating with two opposed pintle ports alternately as said cylinder barrel rotates, a plurality oi. cylinders arranged in said cylinder barrel and each communicating with a cylinder port, a piston fitted in each cylinder, means ior reciprocating said pistons during rotation of said cylinder barrel, means tor reversing said pump to thereby reverse the direction of flow through said pintle ports, fluid channels forv connecting said main ports to an extemaiv circuit, means for connecting one 01' said auxiliary ports to said circuit, means for connecting the other auxiliary port to a source of liquid supply, and means for reversing said connecting means.

10. A reversible difierential pump, comprising a valve shaft or pintle having two opposed main ports and two opposed auxiliary ports formed therein; a rotatable cylinder barrel iournaled upon said pintle and having a plurality of cylinder ports arranged therein in two circular rows, the ports in each row communicating with two 1 opposed pintle ports alternately as said cylinder barrel rotates, a plurality of cylinders arranged in said cylinder barrel and each communicating with a' cylinder port, a piston fitted in each cylinder. means for reciprocating said pistons during rotation of said cylinder barrel, means for reversing said pump to thereby reverse the direction of flow through said pintle ports, fluid chan-- nels for connecting said main ports to an external circuit, means including a valve for connecting one 01' said auxiliary ports to said circuit and the other auxiliary port to a source of liquid supply, and means responsive to a reversal of barrel engaging said valve member and havin a plurality of cylinder ports arranged therein in two circular rows, the ports in each row communicating with one intake port and one dis-,

charge port alternately as said cylinder barrel rotates, a plurality of cylinders arranged in said cylinder barrel and each communicating with a cylinder port, apiston fitted in each cylinder,

means for reciprocating said pistons during rotation of said cylinder barrel, means for reversing said. pump to thereby reverse the direction offlow through said pintle ports, means for connecting one of each 01- said intake and discharge ports to an external circuit, and means ior connecting eachof the other two pintle ports to said circuit and to a separate source of liquid flow through said pintle ports for shifting said valve.

11. A pump, comprising a valve shaft or pintle I provided in one side thereof with a discharge port and in the opposite side thereoi with two intake ports having no communication with each other, a rotatable cylinder barrel ioumaled upon vsaid pintle and having a plurality of cylinder ports arranged therein in two circular rows, the ports in one row communicating with one oi said intake ports and said discharge port alternately and the ports in the otherrow communicating with the other 0! said intake ports and said discharge port alternately during rotation oi said cylinder barrel, a plurality 0! cylinders arranged in said cylinder barrel and each communicating with a cylinder port. a piston fitted in each cylinder, meansior reciprocating said pistons during rotation of said cylinder barrel, and means including a valve ior selectively connecting said intake ports to separate sources of liquid supply or to a single source.

. JAMES K. DOUGLAS. 

